Outbreak of Tularemia in a Group of Hunters in Germany in 2018—Kinetics of Antibody and Cytokine Responses

Abstract

In November 2018, an outbreak of tularemia occurred among hare hunters in Bavaria, Germany. At least one infected hare was confirmed as the source of infection. A number of hunting dogs showed elevated antibody titers to Francisella tularensis, but the absence of titer increases in subsequent samples did not point to acute infections in dogs. Altogether, 12 persons associated with this hare hunt could be diagnosed with acute tularemia by detection of specific antibodies. In nine patients, the antibody and cytokine responses could be monitored over time. Eight out of these nine patients had developed detectable antibodies three weeks after exposure; in one individual the antibody response was delayed. All patients showed an increase in various cytokines and chemokines with a peak for most mediators in the first week after exposure. Cytokine levels showed individual variations, with high and low responders. The kinetics of seroconversion has implications on serological diagnoses of tularemia.

Epidemiological investigation of a tularaemia outbreak after a hare hunt in Bavaria, Germany, 2018

“…Every participant provided at least one blood sample, taken at least two weeks after the initial exposure, allowing this as a minimum time window for antibody development and detection (Jacob et al., 2020; Koskela & Salminen, 1985). The Consiliary Laboratory (CL) for Tularaemia at the Robert Koch Institute (RKI) tested all samples, including those initially tested by the local clinic.…”

“…The CL used this outbreak as an opportunity to add to the scarce knowledge regarding seroconversion after contact to F. tularensis . Therefore, the CL obtained further samples of the initially hospitalized group of hunting participants and closely monitored their serology (Jacob et al., 2020).…”

“…Additionally, a local veterinary practice collected samples of involved dogs. The CL tested throat swabs and EDTA blood via specific real‐time PCR and serum for the detection of antibodies against F. tularensis (Jacob et al., 2020).…”

“…Here, we report the epidemiological outbreak investigation. A manuscript focussing on laboratory testing in this outbreak has been published elsewhere (Jacob et al., 2020).…”

Francisella and Antibodies

“…holarctica [34]. Substantial numbers of wild foxes (V. vulpes), raccoon dogs (N. procyonoides), and wild boars (S. scrofa) collected in several areas of Germany, as well as hunting dogs, were positive for antibodies to F. tularensis [35][36][37]. Exposure to wild and domestic animals expressing antibodies to F. tularensis were identified as a risk factor for humans in European parts of Turkey [38,39].…”